Stratified thermal storage tanks enable the generation of energy to be dissociated, with respect to time, from energy use. In particular, in the case of fluctuating energy sources such as, for example, regenerative energies, such a dissociation with respect to time ensures the supply of energy, in particular electrical energy. For the purpose of discharging, stratified thermal storage tanks may be coupled to general steam circuits and/or ORC systems (organic Rankine cycle; ORC). The use of a stratified thermal storage tank coupled to an ORC system thus enables the generation of thermal energy and the output of electrical energy and/or thermal energy, the electrical energy being provided by the ORC system, to be dissociated, with respect to time, at an energy consumer, thereby making it possible, for example, to balance out load peaks in energy demand, such that, overall, the security of supply improves.
A stratified thermal storage tank can be discharged by means of an ORC system. In this case, the heat is transferred, via walls of a heat exchanger, to a working fluid of the ORC system. To ensure the transfer of heat from the stratified thermal storage tank to the working fluid of the ORC system, certain temperature differences are required, as a driving force for the transfer of heat. At the same time, said temperature differences delimit the temperature level of the thermal energy (heat), i.e. its utilizable value, that can be extracted from the stratified storage tank. In addition, structural space that cannot be used for the storage of thermal energy in the stratified thermal storage tank must be made available for the heat transfer surfaces of a heat exchanger.
A stratified thermal storage tank, having a heat exchanger that has heat transfer surfaces, is discharged by means of the ORC system in that a working fluid of the ORC system on the primary side within the heat exchanger absorbs heat from the heat transfer medium of the stratified storage tank (secondary side).
For the purpose of absorbing the heat, it is known from the prior art to route the heat transfer medium of the stratified thermal storage tank through a vaporizer of the ORC system. Furthermore, it is known from the prior art to route the working fluid of the ORC system through a vaporizer that is located inside the stratified thermal storage tank and that is in thermal contact with the heat transfer medium of the stratified thermal storage tank. In other words, the heat from the stratified thermal storage tank is always transferred to the ORC system through a vaporizer, in which vaporization of the working fluid of the ORC system occurs, the vaporizer in the first-mentioned case being located outside the stratified thermal storage tank, and in the second-mentioned case being located inside it. For an efficient transfer of the heat from the heat transfer medium to the working fluid, the vaporizers according to the prior art have extensive heat transfer surfaces, which, on the one hand, require a large structural space and, on the other hand, reduce the cost effectiveness of the stratified thermal storage tank, owing to the high investment costs.